Lightproof seam and a method of making the same



Sept. 8, 1953 .H. F. BURKHARD 2,651,049

LIGHTPROOF 'SEAM AND A METHOD OF MAKING THE SAME Filed Sept. 50, 1949 lllllllllllllllll flemy F fiurlriz aroZ Patented Sept. 8, 1953 UNITED STATES PATENT OFFICE LIGHTPROOF SEAM AND A METHOD OF MAKING THE SAME (Granted under Title 35, U. S. Code (1952),

sec. 266% The invention described herein, if patented, may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to light-proof seams and a method of making the same, and is particular- 1y useful in the manufacture of portable lightproof tents or bags which are necessary to envelop Signal Corps facsimile equipment by which the pick-up signals are photographed and then developed; however, the invention may be employed wherever it is necessary to have a textile seam impervious to light rays.

When thick, coarse material such as canvas is stitched, tiny holes are formed where the sewing machine needle penetrates the fabric. These tiny holes permit sufiicient light to enter to affect the photographic operation of the receiver, and also to damage sensitive film, in the event the bag is used as a dark room or developing cabinet.

Among other objects, the invention aims to provide a seam which is light-proof even when subjected to considerable stress, which can be sewed on an ordinary sewing machine, and which makes linings unnecessary, therefore reduces material and labor costs. Seams embodying the invention are formed from non-strategic textile materials and require no particular skill in their making.

In the accompanying drawings showing three forms of the invetnion,

Figs. 1, 2 and 3 are detail sections showing the successive steps of forming a light-proof seam according to the invention;

Fig. 4 is a detail section showing a slightly different seam;

Figs. 5 and 6 are detail sections showing the successive steps of forming a light-proof connection between a flap and a bag;

Fig. 7 is an elevation of part of the bag, with a part of its wall broken away to show the flap and its connection with the bag;

Fig. 8 is a perspective of the bag seen from the sleeve end.

The bag Ill is made of heavy canvas or other coarse cloth, has a pair of flexible sleeves II at one end through which the arms of the operator are thrust to permit working the apparatus placed within the bag, a collapsible metal frame (not shown) being employed to support the bag from within so that freedom of movement of the hands is possible. Swingable within the bag is a flap 82 (Fig. '7) which is attached at its top edge to the bag in a manner to be described and normally 2 closes the openings which the inner ends of the sleeves surround. The sleeves H also inclose inner drawstring-tightened sleeves (not shown;

' these and'other details of the bag construction form no part of my invention, which is directed to light-proof seams as already stated.

To form a light-proof seam as at L (Fig. 8) between the top T of the bag and a side S, the fabric pieces to be united are placed flat against each other with the edges even, as shown in Fig. 1, then are double-stitched together as indicated at [3. If there are not two pieces, and merely a corner is desired, the material is folded and double-stitched as before through the two thicknesses, to make a mock seam. A binding strip I4 is then placed over the stitched seam (or mock seam) and is stitched thereto, as at l5, the stitching 15 being closer to the edges of the two pieces (or closer to the line of fold) than the stitching l3, as shown in Fig. 2. Finally, the cloth is reversed so that the seam or mock seam is wholly on the inside, when the parts are as viewed in Fig. 3. The seam so formed is completely lightproof as the tiny holes along the double stitching 13 are completely masked by the binding strip [4 even if the fabric pieces are subjected to a considerable stress tending to separate them at the seam.

Fig. 4 shows a seam L formed by uniting the inner end of sleeve l I to an end wall E of the bag, said seam being circular as will be understood from Fig. 8. It is exactly like seam L except that it is on the outside instead of inside, and like seam L is completely light-proof.

Figs. 5 and 6 illustrate the manner of securing flap l2 to the interior of the bag. First flap l2 and wall E are stitched together as shown at it, then the flap is folded down to inclose stitching l6 and is hemmed by stitching H below the stitching IS. The flap is thus free to swing from stitching l6, yet the tiny holes in said stitching will be covered. This form of the invention requires no separate binding strip, and only two lines of stitching.

In the forms of Figs. 3 and 4, the seams L and L are light-proofed by the use of an extra strip of textile material M which envelopes the seam and is secured to it by stitching which secures the extra strip in a light-excluding position. This binding strip I4 is of such inherent stiffness that it maintains its position on the seam in light-excluding position even though secured by only one line of stitching 15. In the form of Figs. 6 and 7 one of the two textile pieces which are united by stitching is folded down and sewed to itself to make a light-intercepting hem. The result is the same in either case: the pin-holes made by the needles are completely blocked off by a layer of light-impervious material.

Having described three forms of the invention, what I claim as new and desire to secure by Letters Patent is:

1. A light-proof seam consisting of two thicknesses of fabric laid flat and stitched together along a line spaced from the edges of both fabrics, 10

one thickness of fabric beingiolded back to form a hem which incloses said line of stitching and stitching securing the edged the folded back portion only to the same thickness of fabric.

2. A light-proof seam or-mock seammmpri msis two thicknesses of opaque fabric laid flat one on top of the other and stitched together, anopaque binding strip inclosing the edges of the two fabric thicknesses and also inclosing the stitching which binds said two fabric thicknesses together, and 20 stitching uniting the binding strip to said two fabric thicknesses along a line between said stitching which unites the-two fabric thicknesses and the edges of said two fabric thicknesses, the

nesses is intercepted and barred by the opaque binding strip itself.

HENRY F. BURKHARD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,045,231 Whitley Nov. 26, 1912 1314-3108 Lewis Aug. 26, 1919 .:l,"5A7,961 Schmolze July 28, 1925 1,849,514 Edelman Mar. 15, 1932 FOREIGN PATENTS Number Country Date 217,822 GreatBritain 1. June 26, 1924 485,802 Germany June 9, 1928 

